Trains, busses, airplanes and Personal Area Networks (PANs) are examples of use cases where moving network technologies can be applied. A moving wireless network is a cluster consisting of Mobile Network Nodes (MNNs) and Mobile Routers (MRs). A Mobile Router routes IP traffic between a MNN and the Internet (or other IP network). The Mobile Router acts as an access point for the MNN. A Mobile Router may be connected to another moving network or directly to the Internet via an access point (AP). In the former case, a set of nested mobile networks results. The IETF RFC 3963 proposes a Network Mobility (NEMO) protocol according to this architecture.
According to IETF RFC 2461, a Mobile Router broadcasts Routing Advertisement (RA) messages to advertise its existence and to inform MNNs that it provides a mobile routing service. The RAs may contain an operator identifier, for example, to aid selection of an appropriate network by a user. When a MNN finds a suitable Mobile Router, the MNN triggers an attachment exchange with the Mobile Router.
It will be appreciated that when a Mobile Router changes its point of attachment to the Internet, or is handed-off to another Mobile Router, the locations (i.e. IP addresses) of all of the downstream MNNs will change. In order to maintain service continuity during and after hand-off of a Mobile Router, some mechanism is required in order to ensure that data sent from peer (or correspondent) nodes involved in a communication session with the MNN is sent to the MNN at the node's new location. The approach adopted by NEMO involves the creation of a tunnel between the Mobile Router and some home router (or “home agent”) within the fixed network. All traffic sent from a Peer Node to a MNN (and possibly traffic sent in the reverse direction) is routed through the tunnel. When the Mobile Router changes its location, it sends an update to the home router. It may be possible for the MNN to delegate responsibility for location update signalling to an upstream Mobile Router. The key point however is that the network prefix used by the MNN remains unchanged as the Mobile Router moves.
A Mobile Router performs home registration of its upstream or “egress” interface as described in the MIPv6 specification to allow for changes in the point of attachment of the interface to the Internet. When the Mobile Router uses multiple egress interfaces it can have more than one home registration at the same time. This is described in the IETF monami6 working group specification related to multiple care-of-addresses (MCoA).
As well as having multiple egress interfaces, a MR may provide multiple downstream or ingress interfaces. The MR must allocate a different network prefix to each of the various ingress interfaces. These multiple network prefixes must be registered with the HA in addition to the normal MIPv6 home registration. MNNs or “hosts” attached to the ingress interface of the Mobile Router configure IPv6 addresses using the prefix appropriate for the chosen interface, and the Mobile Router tunnels all traffic from the MNNs attached to the ingress interface to the Home Agent (HA) of the Mobile Router. The HA then sends this traffic to the Internet. All traffic which is addressed to a network prefix delegated to an ingress interface of the Mobile Router arrives at the HA, which intercepts the traffic and forwards it to the Mobile Router which in turn routes it to the correct ingress interface.
When a Mobile Router has more than one home registration (i.e. it has multiple egress interfaces) it also has more than one route between the HA and itself. The traffic characteristics of these different paths between the HA and Mobile Router can be quite different. However, MNNs attached to the ingress interface(s) of the Mobile Router do not know anything about the egress interfaces of the Mobile Router and what kind of services the Mobile Router can offer through these. In addition, even if a MNN attached to an ingress interface of the Mobile Router could influence the choice of egress interface through which outgoing packets are routed, it is not easy to see how the MNN could influence the downlink path that packets take from the HA to the Mobile Router.